Why's my phone displaying "phone overheating" constantly?

[AC Question]

I'm in serious trouble with my phone. My Galaxy S6 active is displaying "phone overheats" despite it being at normal temperature. I checked the temperature of the components of the phone with an app and it say the battery is at 90C! Close to the boiling temperature of water! I tried to clean the cache and it didn't help. It even says it may have a risk of catching on fire when I plugged it in. I'm still cooling it down. I can't tell if it is a software error or a hardware failure. Any help? I have some important info on the phone.